In recent years, portable terminals which are capable of connecting to a plurality of heterogeneous communication networks, such as a mobile phone network and a wireless local area network (LAN), as a standard function have come to be widely utilized. With such a portable terminal, communication can be continuously performed among the plurality of communication networks, by properly switching the communication network (communication channel) to be connected or utilized (hereinafter referred to as “handover”).
Regarding the technique related to the handover among the plurality of communication networks, Patent Literature 1 discloses a technique that enables the handover to be stably performed between the mobile phone network and the wireless LAN, without interrupting data communication. According to the cited document, the communication network is switched to the wireless LAN when the reception level of the wireless LAN continuously exceeds a threshold for a predetermined period of time while the terminal is connected to the mobile phone network, and the communication network is switched to the mobile phone network when the reception level of the wireless LAN remains below the threshold for a predetermined period of time while the terminal is connected to the wireless LAN. In addition, the traffic during the communication is monitored, and the communication network is switched between the mobile phone network and the wireless LAN when the traffic is continuously suspended for a predetermined period of time.
With the conventional technique cited above, generally, once the connection is established at the communication network level, the communication network is switched irrespective of whether the connection has been completed at the application level. The communication network level refers to, for example, a transport layer or lower layers and the application level refers to an application layer, in the protocol stack of the transmission control protocol/internet protocol (TCP/IP). Accordingly, such a case may arise that the connection has not been completed at the application level despite the connection having been completed at the communication network level, and hence the application is unable to make communication until the connection is completed at the application level, or until switching to the communication network connected thus far or reconnection is completed after the failure in connection at the application level. Such a situation will be described in further detail, with respect to the case of switching the communication network from the mobile phone network to the wireless LAN, as an example.
When the portable terminal, which is already connected to the mobile phone network, attempts to connect to a backbone network via an access point and then to the internet or the like via a gateway, a predetermined procedure referred to as “association at network level” is performed between the portable terminal and the access point so as to allow the access point to recognize the presence of the portable terminal, in the wireless communication system based on Institute of Electrical and Electronics Engineers (IEEE) 802.11 Standard.
It is also a common practice that a procedure referred to as “authentication at application level” (for example, web authentication) is performed between the portable terminal and the gateway so as to allow the gateway to identify the user, so that only the portable terminal of the identified user is connected to the internet or the like.
FIG. 17 is a chart showing an operation sequence of the conventional wireless LAN communication system.
The portable terminal acquires from a target list an extended service set identifier (ESSID) of the network to which a connection is attempted, and broadcasts a probe request including the ESSID (step S1700).
The access point returns a probe response when the ESSID in the received probe request is the same as its own ESSID or “ANY” (step S1702). The probe response includes parameters such as a basic service set identifier (BSSID), an encryption method, an authentication method, and a communication rate of the access point.
When the portable terminal fails to receive the probe response, the portable terminal broadcast a probe request including another ESSID (step S1700).
Upon receipt of the probe response, the portable terminal determines whether the BSSID included in the probe response is registered in an exclusion list. When the BSSID is registered in the exclusion list, the portable terminal broadcast a probe request including still another ESSID (step S1700).
When the access point is not identified through the mentioned procedure, the portable terminal initializes the exclusion list (deletes the registered BSSID), and then repeats the mentioned procedure.
When the BSSID is not registered in the exclusion list, the portable terminal transmits an authentication request to the access point (step S1704).
The access point determines whether the portable terminal may be authenticated using a predetermined algorithm, and returns an authentication response including the decision (step S1706). Generally, the authentication is performed using the media access control (MAC) address of the portable terminal as an identifier.
Upon confirming the authentication by the access point, the portable terminal transmits an association (connection) request to the access point (step S1708). The association request includes parameters such as the ESSID, a support report, and whether or not polling is necessary.
The access point returns an association response, upon confirming that the MAC address is the authenticated one and that all the parameters in the received association request correspond to the access point (step S1710).
When the connection is established at the communication network level and the communication network is switched from the mobile phone network to the wireless LAN through the procedure described above, the portable terminal is enabled to connect to the backbone network via the access point and transmits a data frame. At this point, however, the user has not been authenticated by the gateway and the connection has not been completed at the application level, and therefore the portable terminal is unable to achieve connection to the internet or the like via the gateway. At this point, the connection to the mobile phone network may or may not be disconnected.
The portable terminal transmits a page acquisition request including the uniform resource locator (URL) of the log-in page, to the gateway (step S1712).
The gateway returns the page corresponding to the URL in the page acquisition request, i.e., the log-in page (step S1714).
The portable terminal transmits the authentication request to the gateway (step S1716). The authentication request includes parameters such as the identification (ID) number of the user and a password. Such data may be automatically extracted from a setup file or manually inputted by the user.
The gateway transfers the received authentication request to an authentication server (step S1718).
The authentication server determines whether the user may be authenticated on the basis of the ID and the password in the received authentication request, and returns the authentication response including the decision (step S1720).
The gateway transfers the received authentication response to the portable terminal (step S1722).
When the user is authenticated by the gateway and the connection is completed at the application level through the mentioned procedure, the portable terminal is enabled to connect to the internet or the like via the gateway, and transmit the connection request to the server (step S1724).